noise coupling

[sbourdeauducq]

Transferred from m-labs/artiq#2226 (GitHub does not allow moving issues between organizations)

"I am trying to use the Fastino card as an analog input for my circuit. In addition, I am using the "DIO-SMA" card to generate the digital signals needed to control my circuit. However, unfortunately, the Fastino output is very noisy and does not match the documentation. I started debugging my setup to find the noise sources.

This support question is focusing on a single type of noise that I am finding difficulty to solve.

Whenever I connect any connector to the digital card pins I see spikes on my Fastino output signals. The state of the digital pin does not seem to mater on the coupled noise. First picture shows the output digital signal (yellow) while in high state. Second picture shows the output digital signal (yellow) after power-up (should be in high z state). But in both cases, the Fastino output (blue) shows 100mV periodic noise spikes. For both cases, the oscilloscope channels are AC coupled."

[...]

[gkasprow]

MohammadAbuzahra Did you manage to connect the Sinara box to the DC bench supply?

[MorganTL]

Using a kasli, DIO-SMA and Fastino, I can replicate this issue by connecting the DIO-SMA(yellow channel) and Fastino(blue channel) to an oscilloscope and powered the kasli using XP power AKM65US12

MohammadAbuzahra Did you manage to connect the Sinara box to the DC bench supply?

I also changed out the XP power psu to a linear bench top power supply Instek GPP-4323, the switching noise still remain

Any other workaround I should try?

[gkasprow]

Get rid of DIO SMA and use non isolated version like DIO MCX. Isolated DIOs are not intended for low noise applications because they have dc/dc converters which inject noise between primary and secondary side.